A disease affecting Japanese and American children under the age of 5 has stumped scientists for 50 years. It spreads rapidly, inflames the blood vessels, and causes heart damage to build quietly over several decades. But while doctors have known the disease’s symptoms, its origin has remained unknown.

In 2011, Xavier Rodó of the Catalan Institute of Climate Sciences found a correlation between the number of children carrying the illness, known as Kawasaki disease, and the intensity of large-scale wind currents coming from the farmlands of northeastern China.

Now, he and his colleagues have identified a possible disease-causing agent that the wind is carrying. After ruling out industrial pollutants, viruses, and pollen, Rodó has proposed in a new study that a fungus light enough to cross the Pacific on prevailing winds could be the cause of the disease. Pinpointing this possible agent helps buoy the wind hypothesis, since before there was no evidence for how the wind might be causing the disease.

After sending a plane to collect wind samples arriving from China, the only thing that Rodó could identify was fungal spores belonging to a group called Candida. Fungal spores are light enough to travel large distances. For instance, microbes have been known to go as high up as the upper stratosphere, as they get lifted by strong winds or volcanoes. Candida spores can also trigger immune reactions. But there isn’t enough data to confirm the cause is Candida yet.

If the wind-borne hypothesis is true, and spores (either of Candida or asimilar fungus) are indeed riding on gusts of wind, then it’s an unprecedented discovery. Some pathogens like valley fever turn up after turbulent dust storms or spore-shaking earthquakes. And the fungus Aspergillus sydowii may drift via African dust storms, spurring coral disease in the Caribbean. But the Kawasaki disease would be the first documented case of a human pathogen crossing thousands of miles without the help of a cargo ship or other manmade means.

Back in 2012, Jennifer Frazer explored the possibility of an airborne pathogen traveling over vast distances in Nature. She interviewed Jane Burns, director of the Kawasaki Disease Research Center:

Certainly the group’s analysis would fly in the face of conventional wisdom if the disease agent proves to be a living organism, says Burns. Microbiologists have generally assumed that ultraviolet radiation and the near-cryogenic temperatures at high altitude will annihilate any infectious microbes before they can make it across an ocean. But maybe not, she says. “My background is molecular virology. When I preserve my viruses in the lab, what do I do? I desiccate them and freeze them at −80°C. Well, hello! Those are the conditions up in the troposphere.”

Besides, says Burns, wind is often full of dust. “If you take a dust particle and look at it under the electron microscope, it’s like a whole universe,” she says. “It’s got nooks and crannies and valleys and peaks”, any of which could shelter a microbe or two from solar ultraviolet.

The authors of the paper make clear that discovering Candida in wind currents “can only be reported here as providing support for the concept and feasibility of a windborne pathogen rather than implicating any particular organism.” So while there’s been no direct detection of Candida in patients, the study does show that very long-distance pathogenic “flights,” perhaps of a fungus like Candida, are possible.

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